Rotary joint device, motor, and machine tool

A rotary joint device comprising:

• a rotary-side joint having a tubular shape and a first hole through which liquid is to flow in an axial direction, the rotary-side joint being rotatable in a circumferential direction;
• a fixed-side joint having a tubular shape and an end face at one end facing an end face at one end of the rotary-side joint, the fixed-side joint being configured to reciprocate in the axial direction of approaching and separating from the rotary-side joint, the fixed-side joint further having a second hole in the axial direction that communicates with the first hole of the rotary-side joint in a state where the fixed-side joint is in contact with the rotary-side joint;
• an attachment having an inner peripheral surface, the attachment being fixable to another member, the inner peripheral surface defining a third hole through which the liquid is to flow and into which the other end of the fixed-side joint is inserted;
• a DLC (diamond-like carbon) film provided on an outer peripheral surface of the fixed-side joint;
• and
• an elastic member interposed liquid-tight between the inner peripheral surface of the attachment and the DLC film, the elastic member being slidable with respect to the DLC film when the fixed-side joint moves in the axial direction with respect to the rotary-side joint,
• wherein the DLC film is provided in a contact area where the elastic member contacts on the outer peripheral surface.